Remove unused includes/externals

Test: mm
Change-Id: I4b88602b7d0a18664cbeddfa9854e589c2886e1a
diff --git a/linker/linker.cpp b/linker/linker.cpp
index f8531b6..291e242 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -44,8 +44,6 @@
 #include <vector>
 
 // Private C library headers.
-#include "private/KernelArgumentBlock.h"
-#include "private/ScopedPthreadMutexLocker.h"
 #include "private/ScopeGuard.h"
 
 #include "linker.h"
@@ -66,11 +64,6 @@
 #include "android-base/stringprintf.h"
 #include "ziparchive/zip_archive.h"
 
-extern void __libc_init_globals(KernelArgumentBlock&);
-extern void __libc_init_AT_SECURE(KernelArgumentBlock&);
-
-extern "C" void _start();
-
 // Override macros to use C++ style casts.
 #undef ELF_ST_TYPE
 #define ELF_ST_TYPE(x) (static_cast<uint32_t>(x) & 0xf)